1. Field of the Invention
The present invention relates to a projection device, an image correction method, and a computer-readable recording medium.
2. Description of the Related Art
A projection device such as a projector device is known which drives display elements based on an input image signal and projects an image relating to the image signal on a projection face of a projection medium such as a screen or a wall face. In such a projection device, in a case where a projection image is projected not in a state in which an optical axis of a projection lens is perpendicular to the projection face but in a state in which the optical axis of the projection lens is inclined with respect to the projection face, a problem of a so-called trapezoidal distortion in which a projection image originally projected in an originally approximate rectangular shape is displayed to be distorted in a trapezoidal shape on the projection face occurs.
Accordingly, conventionally, by performing a trapezoidal distortion correction (keystone correction) for converting an image that is a projection target into a trapezoidal shape formed in a direction opposite to that of the trapezoidal shape formed in the projection image displayed on the projection face, a projection image having an approximately rectangular shape without any distortion is displayed on the projection face.
For example, in Japanese Patent Application Laid-open No. 2004-77545, a technology for projecting excellent video for which a trapezoidal distortion correction has been appropriately performed onto a projection face in a projector also in a case where the projection face is either a wall face or a ceiling is disclosed.
In such a conventional technology, when a trapezoidal distortion correction (keystone correction) is performed, an image is converted into a trapezoidal shape formed in a direction opposite to a trapezoidal shape generated in a projection image according to a projection direction, and the converted image is input to a display device, whereby the keystone correction is performed. Accordingly, on the display device, an image having the number of pixels that is smaller than the number of pixels that can be originally displayed by the display device is input in the trapezoidal shape formed in the opposite direction, and a projection image is displayed in an approximately rectangular shape on the projection face onto which the projection image is projected.
In the conventional technology as described above, in order not to display an area of the periphery of the projection image onto which the approximately rectangular-shaped original projection image is projected, in other words, a differential area between the area of the projection image of a case where no correction is made and the area of the projection image after the correction on the projection face, image data corresponding to black is input to the display device, or the display device is controlled not to be driven. Accordingly, there is a problem in that the pixel area of the display device is not effectively used. In addition, there are cases where the brightness of the actual projection area decreases.
Meanwhile, recently, in accordance with wide use of high-resolution digital cameras, the resolution of video content is improved, and thus, there are cases where the resolution of the video content is higher than the resolution of a display device. For example, in a projection device such as a projector that supports up to full HD of 1920 pixels×1080 pixels as an input image for a display device having resolution of 1280 pixels×720 pixels, the input image is scaled in a prior stage of the display device so as to match the resolution such that the whole input image can be displayed on the display device, or a partial area of the input image that corresponds to the resolution of the display device is cut out and is displayed on the display device without performing such scaling.
Even in such a case, in a case where projection is performed in a state in which the optical axis of the projection lens is inclined with respect to the projection face, a trapezoidal distortion occurs, and accordingly, it is necessary to perform the trapezoidal distortion correction, and similar problems occur at that time.
The present invention is devised in consideration of the description presented above, and an object thereof is to provide a projection device, an image correction method, and a computer-readable recording medium capable of easily acquiring an appropriate projection image.